1. Field of the Invention
The present invention relates in general to the field of information handling system circuit board test, and more particularly to a multi-stage in circuit test with strain management.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Information handling systems are typically built from a variety of components that communicate through a circuit board, such as a printed circuit board (PCB). The circuit board communicates signals, power and ground through wire lines formed in a nonconductive material, such as copper wires printed in laminated layers of plastic. Once the wire lines are prepared and the circuit board lamination is complete, electronic components are connected to the circuit boards in defined positions, such as by soldering electronic components to exposed connection points on the circuit boards. Often, processors and other large components are coupled to the circuit board with sockets that have mechanical coupling devices to hold processors in place. For example, a ball grid array (BGA) socket solders into a circuit board to establish electrical communication between wire lines of the circuit board and balls laid out on the socket surface. A processor is placed over the balls so that processor contacts interface with the balls and, in turn, with the circuit board wire lines. A load mechanism placed over the processor presses against the top of the processor to hold the processor contacts in place relative to the socket balls.
Circuit boards generally represent a small portion of the overall cost of an information handling system, however, if a circuit board includes a fault then the more expensive components will often fail in unpredictable manners. For this and other reasons, circuit boards are typically tested for faults before assembly of components to the circuit board with a process generally referred to as in circuit testing (ICT). During in circuit testing, electrical probes test a circuit board to check for faults such as shorts, opens, resistance, capacitance and other indicators that will show whether the circuit board is correctly fabricated. Generally, a “bed of nails” configuration of probes is brought into contact with testing pads formed on the circuit board. Probes are brought into contact with testing nodes by pressing the circuit board against the probes. Typically, the circuit board is brought into contact with probes by creating a vacuum in a test space that pulls the circuit board downward into the probes, such as with the Agilent i3070 tester. In some cases, the circuit board is tested in multiple stages by stopping the circuit board's vacuum-induced motion after a first distance to provided contact with a first set of spring-loaded probes, and then removing the stops to allow the vacuum to pull the circuit board downwards into a second set of probes. The first set of probes is longer than the second set of probes and include spring loading so that the first set of probes recede downward with the circuit board as the board lowers against the second set of probes.
In order to varying the distance that a circuit board travels during testing, stops are typically inserted along the edges of the load plate at the point where the first set of probes contact the circuit board. After completion of testing by the first set of probes, the stops are withdrawn to allow the circuit board to move so that the vacuum pulls the circuit board downward to the second set of probes. One difficulty that arises in such multi-stage testing is that, during the first stage of testing, the vacuum exerts a force across the circuit board and load plate that introduces flexion distal the stops. The downward force tends to bow the circuit board about its center point, which introduces strain to the circuit board. Strain across the circuit board transfers to wire lines and solder so that cracks and other faults may develop as a result of the testing. The amount of strain increases as the surface area of the circuit board increases and the thickness of the circuit board decreases. In some instances, a bent circuit board becomes unsuitable for use in an information handling system. In other instances, cracks form at socket joints and in other portions of the socket as the circuit board flexes relative to a stiff socket structure.